Recent advances in the methodology, optimisation and application of MEEKC

Abstract

MEEKC is an electrodriven separation technique. Oil-in-water microemulsions (MEs) and to a lesser extent water-in-oil MEs have been used in MEEKC as BGEs to achieve separation of a diverse range of solutes. The more common (oil-in-water) MEs are composed of nanometre-sized droplets of oil suspended in an aqueous buffer. Interfacial tension between the oil and aqueous phase is reduced close to zero by the presence of a surfactant and a co-surfactant. MEEKC is capable of providing fast and efficient separations for a wide range of acidic, basic and neutral, water-soluble and -insoluble compounds. This review details the advances in MEEKC-based separations from the period 2006 to 2008. Areas covered include online sample concentration, chiral separation, suppressed electroosmosis MEEKC, MEEKC-MS, and the use of MEEKC in predicting migration behaviour and solute characteristics. A fundamental introduction to MEEKC, along with the presentation and discussion of recent applications is also included.

Advanced CE for chiral analysis of drugs, metabolites, and biomarkers in biological samples

“…On the other hand, the formation of stable complexes of hydrophobic analytes (that are many of the drugs) can be accomplished in aqueous solutions using pseudostationary phases with proper hydrophobic bounding sites. Thus, typically, chiral micelles or chiral mixed micelles (in MEKC) and microemulsions (in MEEKC) help solving additional problems in chiral CE, such as enantioseparation of hydrophobic analytes in aqueous buffers [104,167,168,171]. In this field, chiral micelle polymers appeared recently as a very attractive alternative to the conventional micelle systems offering significant benefits not only in separation (fast complexing kinetics) but also detection (especially MS) schemes (see Section 2.1.8.).…”

“…), the chiral CE separation systems with high performance variability can be created. Thus, the separations of enantiomeric couples of a wide scale of polarities, charges, and sizes can be easily accomplished [42,[102][103][104][166][167][168], see examples in Section 2.2.4 and Table 1. In CE, the improved separation enantioselectivity of charged solutes can be observed, in many cases, with oppositely charged chiral selectors compared with neutral ones as it was mentioned from the complex formation point of view in Section 2.1.1 (where CDs were used as examples).…”

Advances in the theory and application of MEEKC

“…Kahle and Foley have completed extensive studies involving the effects of single, dual and triple chiral component ME systems [11,[54][55][56][57]. A summary of their findings are covered in previous reviews [1,57]. Interested readers are also encouraged to consult a review by Preinerstorfer et al [58], dedicated to enantioselective separations in CE, MEKC, MEEKC and CEC.…”

“…The presence of the co-surfactant and Richie Ryan 1 Sheila Donegan 1 particularly the oil results in MEs having great solubilising power for both water-insoluble and water-soluble compounds. They therefore offer the ability to directly solubilise hydrophobic samples and matrices, such as creams and waxes, without lengthy pre-extraction steps.…”

Analysis of nucleosides and nucleobases by microemulsion electrokinetic capillary chromatography coupled with field-amplified sample injection

“…However, the close isoelectric points (pIs) of nucleosides and analogues make them difficult to separate by conventional CE method. 26 By changing the surfactant concentration and subsequently altering the charge density of the aggregate, MEEKC is granted the ability to extend the elution range of the separation, 27 which render MEEKC the high efficiency separation of charged or neutral analytes covering a wide range of water solubility 26 and offers a large and exible separation capability for various analytes. 20-23 MEEKC combines chromatographic partitioning between two phases and electrokinetic migration.…”